1. Field of Invention
The present invention generally relates to filtering devices, and more particularly to a filtering device with a crossflow fan and a spoiler to filter slurry in the manufacturing of semiconductor devices.
2. Description of Related Art
With the steady improvement of integration in semiconductor devices, demand for more interconnects is getting higher due to the size diminishment of metal-oxide-semiconductor (MOS) transistors. It is therefore a common way to use at least two metal layers in designing integrated circuits. It is also very important, however, to have a planarization process on the rough surface of a wafer, so as to facilitate the manufacturing process of the multi-level interconnects and make the transferred wiring patterns more accurate. In addition the planarization of a wafer is the major factor affecting aligning accuracy in an alignment system. If the planarization process for a wafer is poorly done, not only the mask can not accurately focus on the wafer in the alignment system, but also the error-prone probability during the manufacturing is significantly increased.
A method of chemical-mechanical polishing (CMP) is regarded as the only technology to provide global planarization in the manufacturing of very-large scale integrated circuits (VLSI), or even ultra-large semiconductor integration (ULSI). Essentially, the CMP is based on a principle similar to a "grinding wheel" in mechanical grinding. With the aid of a reagent, the rough surface of a wafer can then be smoothly ground by using this technology.
The reagent, normally called "slurry" in a CMP process, is a mixture of colloidal silica, or dispersed alumina, with liquids of KOH of strong base and NH.sub.4 OH of strong acid. The dimension of particles, which are extremely hard, in the slurry is ranged from 0.1 to 2.0 .mu.m. Essentially, the particles of extremely high hardness in the slurry are used for grinding the rough surface of a wafer. Basically, the slurry is filtered by a filtering device before transporting to a polishing pad of a CMP machine for grinding, so as to prevent the slurry from scratching the surface of the wafer.
FIG. 1 shows a cross-sectional top view of a conventional filtering device 5. There is a filter 12 used to filter the slurry in the filter housing 10. The slurry in the filter housing 10, used by the CMP machine, is provided through a pipe by a slurry supplier (not shown) via a slurry inlet 14 on one side of the filter housing 10. In addition, the filter 12 comprises an opening, which covers a slurry outlet 16 located at the bottom of the filter housing 10, so that the slurry conveyed to the polishing pad is filtered.
When the CMP grinding is under way, the slurry used to facilitate the CMP processing is continuously supplied through a pipe to the polishing pad via the slurry outlet 16 at the bottom of the filter housing 10.
If the filtering device 5 is designed in this way, the slurry in the filter housing 10 becomes still when the filtering device 5 is idle, that is, the CMP machine is not used for grinding or does not use the slurry. Under this circumstance, it is quite often that the slurry is congealed on the surface of the filter 12 making the filter 12 congested.
Furthermore, larger particles are adhered to the surface of the filter 12 after a certain period of operation, which becomes difficult for the slurry to flow through the filter 12, because of the slow movement of the slurry, even the filtering device 5 is in operation.
The slurry flow to the polishing pad becomes irregular whenever there is congestion in the filter 12. Hence, the productivity efficiency of the CMP machine as well as the lifetime of the filter 12 are reduced.
As a summary, the conventional filtering device 5 has the following disadvantages:
1. The slurry tends to congeal into particles on the surface of the filter 12, which subsequently congests the filter 12, when the filtering device 5 is idle. PA1 2. When there is congestion in the filter 12, the slurry supply to the polishing pad becomes irregular, which affects the productivity efficiency of the CMP machine, and reduces the lifetime of the filter 12. PA1 3. Even in operation mode, the slurry flow becomes slow after a certain period of usage. Larger particles are adhered to the surface of the filter 12, preventing the slurry from passing through the filter 12 smoothly.
In light of the foregoing, there is a need to provide a device for filtering slurry in the manufacturing of semiconductor devices.